Does watch(provider) update children of parent widget? - flutter

I'm trying to update both Pages with one UserInteraction, therefore trying to access the same Stream in both Pages, with the Riverpod library.
Now to explain it further. When I pass the Stream to the CustomerPage I'm able to get the data (the String Anton). and when I click on the Button that triggers the change in FireStore, the String gets updated to "Marco" in the ParentWidget, when I go back to it. But it doesn't change in the CustomerPage unless I reopen the Page via the RaisedButton in the ParentWidget.
But I want it to update after I click the Button on the CustomerPage.
I hope this makes it clearer.
class ParentWidget extends ConsumerWidget{
Widget build(BuildContext context, ScopedReader watch){
Stream<DocumentSnapshot> doc = watch(streamProvider.stream);
return Container(
child: Column(
children: [
Text(doc.name), //Lets say the name is Anton,
RaisedButton(
child: Text(" road to CustomerPage"),
onPressed:(){
Navigator.of(context).pushNamed(RouteGenerator.customerPage, arguments: doc);
},), //RaisedButton
],), //Column
); //Container
}
}
class CustomerPage extends StatelessWidget{
Stream<DocumentSnapshot> docStream
CustomerPage({this.docStream});
Widget build(BuildContext context){
return Column(
children: [
Text(docStream.name) //Here is also Anton
RaisedButton(
child: Text("Change Name"),
onPressed: () {
context.read(streamProvider).changeName("Marco");
},), //RaisedButton
]
); //Column
}
}

On how I've understood so far is that, riverpod allows you to fetch the state of a provider, which basically is a value(?), that's why it's sufficient to just watch it in any Widget you want to access it's data from. There is no need anymore (just speaking for my case), to let Widgets pass the around in the App.
Down below is the solution which i believe to be right.
It also doesn't matter on how many times I call the provider. It's always going to be same Instance. For my case it means, that doc and doc2 are the same.
I hope this makes it clearer.
class ParentWidget extends ConsumerWidget{
Widget build(BuildContext context, ScopedReader watch){
Stream<DocumentSnapshot> doc = watch(streamProvider.stream);
return Container(
child: Column(
children: [
Text(doc.name), //Lets say the name is Anton,
RaisedButton(
child: Text(" road to CustomerPage"),
onPressed:(){
Navigator.of(context).pushNamed(RouteGenerator.customerPage);
},), //RaisedButton
],), //Column
); //Container
}
}
class CustomerPage extends ConsumerWidget{
Widget build(BuildContext context, ScopedReader watch){
Stream<DocumentSnapshot> doc2 = watch(streamProvider.stream);
return Column(
children: [
Text(doc2.name) //Here is also Anton
RaisedButton(
child: Text("Change Name"),
onPressed: () {
context.read(streamProvider).changeName("Marco");
},), //RaisedButton
]
); //Column
}
}

Related

onPressed does not execute Function even after using setState

I created a function below
nextQuestion() {
setState(() {
questionIndex++;
});
print('pressed');
}
I then created the class below and passed in the method above a constructor for an onPressed property
class Answer extends StatelessWidget {
final String answer;
final VoidCallback? selectHandler;
// ignore: use_key_in_widget_constructors
const Answer({required this.answer, this.selectHandler});
#override
Widget build(BuildContext context) {
return ElevatedButton(
onPressed: selectHandler,
child: SizedBox(
width: double.infinity,
child: Center(
child: Text(
answer,
),
),
),
);
}
}
I then used the constructor of the class and passed in the function to update the text on my screen which is in a list with questionIndex as its index
Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: [
Question(question: questions[questionIndex]),
Answer(selectHandler: nextQuestion(), answer: 'Yellow'),
Answer(selectHandler: nextQuestion(), answer: 'Yellow'),
Answer(selectHandler: nextQuestion(), answer: 'Yellow'),
],
),
This is not working/Is not updating the text on my screen after pressing the button
I've recreated the code and it works for me with a few exceptions:
Answer(selectHandler: nextQuestion(), answer: 'Yellow'), is wrong. You have to use selectHandler: nextQuestion (no () after the function)
Use the answer widget inside another stateful widget.
If you did all these and it still doesn't work run flutter clean followed by flutter pub get (close the debug session first)
And if that doesn't work, the problem is with your questions widget.

Dart - Re-using Flutter widgets sometime contains wrong data

I have a Flutter web application that displays multiple user profiles on a card within a Row. The cards can each flip over to reveal more information via this library:
https://pub.dev/packages/flip_card
The application uses WebSockets and receives a JSON list of user details which maps to a User dart class, and as soon as new list arrives on a socket, we create a widget and add it to a widgetList and wrap it in a setState():
webSocket.onMessage.listen((e) {
final List receivedJsonUserList = json.decode(e.data);
final List<User> userListFromSocket =
receivedJsonUserList.map((item) => User.fromJson(item)).toList();
userListFromSocket.forEach((newUser) {
setState(() {
widgets[newUser.user.id] = UserDetails(user: newUser);
widgetList = widgets.entries.map((entry) => entry.value).toList();
});
});
}
}
});
The widget is drawn like this:
#override
Widget build(BuildContext context) {
return ResponsiveBuilder(
builder: (context, sizingInformation) => Scaffold(
drawer: sizingInformation.deviceScreenType == DeviceScreenType.mobile
? NavigationDrawer()
: null,
backgroundColor: Colors.white,
body: Scrollbar(
child: SingleChildScrollView(
child: Column(
children: <Widget>[
Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: widgetList),
],
),
),
),
),
);
}
The code works 90% of the time, but occasionally the wrong data is on the back of a card. So User 1 will have User 2's data on the back, etc.
Am I doing this correctly? Is there an obvious issue with this implementation? I tried to create a seperate widget for each user and it seems to resolve the issue but re-using widgets surely has to be possible.

Flutter : using changeNotifier and provider when the context is not available

I'm trying to use the simple state management described in the Flutter docs, using a ChangeNotifier, a Consumer, and a ChangeNotifierProvider.
My problem is that I can't get a hold a on valid context to update my model (details below...). I get an error:
Error: Error: Could not find the correct Provider above this CreateOrganizationDialog Widget
This likely happens because you used a BuildContext that does not include the provider of your choice. There are a few common scenarios:
The provider you are trying to read is in a different route.
Providers are "scoped". So if you insert of provider inside a route, then other routes will not be able to access that provider.
You used a BuildContext that is an ancestor of the provider you are trying to read.
Make sure that CreateOrganizationDialog is under your MultiProvider/Provider.
This usually happen when you are creating a provider and trying to read it immediately.
Here are extracts of my code:
class OrganizationModel extends ChangeNotifier {
final List<Organization> _items = [];
/// An unmodifiable view of the items in the cart.
UnmodifiableListView<Organization> get items => UnmodifiableListView(_items);
void addList(List<Organization> items) {
_items.addAll(items);
notifyListeners();
}
}
This is my model.
class OrganizationBodyLayout extends StatelessWidget {
Future<void> _showCreateOrganizationDialog() async {
return showDialog<void>(
context: navigatorKey.currentState.overlay.context,
barrierDismissible: false,
child: CreateOrganizationDialog());
}
_onCreateOrganizationPressed() {
_showCreateOrganizationDialog();
}
_onDeleteOrganizationPressed() {
//TODO something
}
_onEditOrganizationPressed() {
//TODO something
}
#override
Widget build(BuildContext context) {
return Container(
child: Column(mainAxisSize: MainAxisSize.max, children: [
ButtonBar(
alignment: MainAxisAlignment.start,
mainAxisSize: MainAxisSize.max,
children: <Widget>[
RaisedButton(
onPressed: _onCreateOrganizationPressed,
child: Text("New Organization"),
),
],
),
Expanded(
child: Container(
color: Colors.pink,
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: <Widget>[
Expanded(
child: ChangeNotifierProvider(
create: (context) => OrganizationModel(),
child: OrganizationListView(),
)),
Expanded(child: Container(color: Colors.brown))
]))),
]));
}
}
A stateless widget that contains a ChangeNotifierProvider just on top of the list widget using the model.
On a button click, a modal dialog is shown, then data is fetched from the network. I should then update my model calling the addList operation.
Below is the code for the stateful dialog box.
class CreateOrganizationDialog extends StatefulWidget {
#override
_CreateOrganizationDialogState createState() =>
_CreateOrganizationDialogState();
}
class _CreateOrganizationDialogState extends State<CreateOrganizationDialog> {
TextEditingController _nametextController;
TextEditingController _descriptionTextController;
#override
initState() {
_nametextController = new TextEditingController();
_descriptionTextController = new TextEditingController();
super.initState();
}
#override
Widget build(BuildContext context) {
return Dialog(
child: Container(
width: 200,
height: 220,
child: Column(
children: [
Text('New organization',
style: Theme.of(context).textTheme.headline6),
Padding(
padding: EdgeInsets.all(8.0),
child: TextFormField(
decoration: new InputDecoration(hintText: "Organization name"),
controller: _nametextController,
),
),
Padding(
padding: EdgeInsets.all(8.0),
child: TextFormField(
decoration:
new InputDecoration(hintText: "Organization description"),
controller: _descriptionTextController,
),
),
ButtonBar(
children: [
FlatButton(
child: new Text("Cancel"),
onPressed: () {
Navigator.of(context).pop();
},
),
FlatButton(
child: new Text("Create"),
onPressed: () {
setState(() {
Future<Organization> organization =
backendCreateOrganization(_nametextController.text,
_descriptionTextController.text);
organization.then((value) {
Future<List<Organization>> organizations =
backendReloadOrganizations();
organizations.then((value) {
var model = context.read<OrganizationModel>();
// var model = navigatorKey.currentState.overlay.context.read<OrganizationModel>();
//model.addList(value);
});
});
});
Navigator.of(context).pop();
//context is the one for the create dialog here
},
)
],
)
],
),
));
}
}
My problem happens at the line
var model = context.read<OrganizationModel>();
Thinking of it, the context available here is the modal dialog box context - so it's kind of logical that the Provider is not found in the widget tree.
However, I can't see how to retrieve the proper context (which would be the one for the result list view, where the Provider is located) in order to get the model and then update it.
Any idea is welcome :-)
Solved (kind of).
The only way I've found to solve this is by making my model a global variable:
var globalModel = OrganizationModel();
And referencing this global model in all widgets that consume it. I can't find a way to find the context of a stateless widget from within a callback in another stateful widget.
It works, but it's ugly. Still open to elegant solutions here :-)
Get_it seems to be elegant way of sharing models across the application. Please check the documentation for the different use cases they provide.
You could do something like the following
GetIt getIt = GetIt.instance;
getIt.registerSingleton<AppModel>(AppModelImplementation());
getIt.registerLazySingleton<RESTAPI>(() =>RestAPIImplementation());
And in other parts of your code, you could do something like
var myAppModel = getIt.get<AppModel>();

Flutter - How to flip the previous card back using FlipCard

After days of search I'm getting help.
I work on a flutter application.
Context:
A grid view feeded with Json
-childs : GridTile with Flipcard in (https://pub.dev/packages/flip_card)
-On tap on GridTile there is a callback to get the selected Item and an animation because of the flipcard onTap
What I would:
When an item is aleready selected (flipcard flipped so we show the back of the card),
And I selected another item of the grid te(so flipcard of this itme also flipped)
I would like to flip back the old selected item Flipcard without rebuild the tree because I would lost the state of the new selected item.
I tried many thing. For example I tried to use GlobalKey on GridTiles to interract with after build but currentState is always null when I want to interact with.
I wonder what is the good practice in this case ?
I hope I was clear :) (I'm french)
Thank you the community!
.
Something to know...
It is possible to interract with the flipcard (child of gridtile) like this
(GlobalKey)
GlobalKey<FlipCardState> cardKey = GlobalKey<FlipCardState>();
#override
Widget build(BuildContext context) {
return FlipCard(
key: cardKey,
flipOnTouch: false,
front: Container(
child: RaisedButton(
onPressed: () => cardKey.currentState.toggleCard(),
child: Text('Toggle'),
),
),
back: Container(
child: Text('Back'),
),
);
}
I'm not sure if I understood your question, but here is an example of how you could use a GridView with FlipCards:
var cardKeys = Map<int, GlobalKey<FlipCardState>>();
GlobalKey<FlipCardState> lastFlipped;
Widget _buildFlipCard(String text, Color color, int index) {
return SizedBox(
height: 120.0,
child: Card(
color: color,
child: Center(
child:
Text(text, style: TextStyle(color: Colors.white, fontSize: 20.0)),
),
),
);
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: Text("FlipCards")),
body: GridView.builder(
itemCount: 20,
itemBuilder: (context, index) {
cardKeys.putIfAbsent(index, () => GlobalKey<FlipCardState>());
GlobalKey<FlipCardState> thisCard = cardKeys[index];
return Column(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
FlipCardWithKeepAlive(
child: FlipCard(
flipOnTouch: false,
key: thisCard,
front: _buildFlipCard("$index", Colors.blue, index),
back: _buildFlipCard("$index", Colors.green, index),
onFlip: () {
if (lastFlipped != thisCard) {
lastFlipped?.currentState?.toggleCard();
lastFlipped = thisCard;
}
},
),
),
RaisedButton(
child: Text("Flip Card"),
onPressed: () => cardKeys[index].currentState.toggleCard(),
)
],
);
},
gridDelegate:
SliverGridDelegateWithFixedCrossAxisCount(crossAxisCount: 2),
),
);
}
class FlipCardWithKeepAlive extends StatefulWidget {
final FlipCard child;
FlipCardWithKeepAlive({Key key, this.child}) : super(key: key);
#override
State<StatefulWidget> createState() => FlipCardWithKeepAliveState();
}
class FlipCardWithKeepAliveState extends State<FlipCardWithKeepAlive>
with AutomaticKeepAliveClientMixin {
#override
Widget build(BuildContext context) {
super.build(context);
return widget.child;
}
#override
bool get wantKeepAlive => true;
}
You need to use a different key for each element of the list, I used a Map in this case.
I also wrapped the FlipCard with a custom FlipCardWithKeepAlive stateful widget that uses AutomaticKeepAliveClientMixin to keep alive the FlipCard while scrolling.
Edit: I updated the code so when you flip one card, the previous card flipped gets flipped back. Basically you need to save the last flipped card and when a new one is flipped, flip the last one and put the new one as last flipped.
The code will make both cards flip at the same time, if you want one card to wait the other use onFlipDone() instead of onFlip(), like this:
onFlipDone: (isFront) {
bool isFlipped = !isFront;
if (isFlipped && lastFlipped != thisCard) {
lastFlipped?.currentState?.toggleCard();
lastFlipped = thisCard;
}
}

Navigator gets the wrong context

I have a flutter application which shows a camera, then scans a qr-code using git://github.com/arashbi/flutter_qrcode_reader and on the call back, I want to navigate to another screen to show the information I get from some query. The problem is, it seems Navigator get a wrong context, so instead of full page navigation, I see the second page pushed inside my first page as a widget.
The build of first page is as follow :
#override
Widget build(BuildContext context) {
Widget main =
new Scaffold(
appBar: _buildAppBar(),
body: Column(
children: <Widget>[
_eventButton ?? new Text(""),
new Center(
child: new Text("Hi"))
],
),
floatingActionButton: new FloatingActionButton(
onPressed:
() {
new QRCodeReader()
.setAutoFocusIntervalInMs(200)
.setForceAutoFocus(true)
.setTorchEnabled(true)
.setHandlePermissions(true)
.setExecuteAfterPermissionGranted(true)
.scan().then((barcode) => _showTicketPage(barcode));
}
,
child: new Icon(Icons.check),
),
);
if (!_loading) {
return main;
} else {
return new Stack(
children: [main,
new Container(
decoration: new BoxDecoration(
color: Color.fromRGBO(220, 220, 220,
0.3) // Specifies the background color and the opacity
),
child: new Center(child: new CircularProgressIndicator(),))
]
);
}
}
The 'Hi' Widget is for debugging, and the navigate method is
void _showTicketPage(var barcode) {
Navigator.push(context, MaterialPageRoute(
builder: (BuildContext context) => TicketScreen(barcode)));
}
After getting the barcode, the second screen - TicketScreen - is pushed under 'Hi' Widget. I didn't even know this was possible to do.
I tried to get the context of the screen, save it to a field var, but that didn't help either.
How can I fix it? I ran out of ideas.